1. Technical Field
The present invention relates to a pattern-forming method.
2. Background Art
In the field of microfabrication (e.g., production of integrated circuit devices), lithographic technology that enables microfabrication with a line width of 0.1 μm or less has been desired to achieve a higher degree of integration. A lithographic process has utilized near ultraviolet rays (e.g., i-line). However, it is difficult to implement sub-quarter-micron microfabrication using near ultraviolet rays. Therefore, use of radiation having a shorter wavelength has been studied to enable microfabrication with a line width of 0.1 μm or less. Examples of such radiation include deep ultraviolet rays (e.g., mercury line spectrum and excimer laser light), X-rays, electron beams, and the like. In particular, technology that utilizes KrF excimer laser light (wavelength: 248 nm) or ArF excimer laser light (wavelength: 193 nm) has attracted attention.
As a resist that is suitable for excimer laser light, various resists (chemically-amplified resist) that utilize a chemical amplification effect due to an acid-dissociable functional group-containing component and a component that generates an acid upon irradiation (exposure) (hereinafter referred to as “acid generator”) have been proposed. For example, a chemically-amplified resist that includes a resin containing a t-butyl ester group of a carboxylic acid or a t-butyl carbonate group of phenol, and an acid generator, has been proposed (Japanese Patent Application Publication (KOKAI) No. 5-232704, for example). This resist utilizes a phenomenon in which the t-butyl ester group or the t-butyl carbonate group contained in the resin dissociates due to an acid generated upon exposure to form an acidic group (e.g., carboxyl group or phenolic hydroxyl group), so that the exposed area of the resist film becomes readily soluble in an alkaline developer.
Such a lithographic process will be required to form a more minute pattern (e.g., a resist pattern with a line width of about 45 nm). A pattern with a line width of less than 45 nm may be formed by reducing the wavelength of the light source of the exposure system or increasing the numerical aperture (NA) of the lens. However, an expensive exposure system is required to reduce the wavelength of the light source. When increasing the numerical aperture (NA) of the lens, since the resolution and the depth of focus have a trade-off relationship, a decrease in depth of focus occurs when increasing the resolution.
In recent years, liquid immersion lithography has been proposed as lithographic technology that can solve the above problems (Japanese Patent Application Publication (KOKAI) No. 10-303114, for example). In liquid immersion lithography, a liquid high-refractive medium (immersion liquid) such as pure water or a fluorine-containing inert liquid is provided on at least on the resist film between the lens and the resist film on the substrate during exposure. In liquid immersion lithography, the optical space (path) is filled with a liquid (e.g., purified water) having a high refractive index (n) instead of an inert gas (e.g., air or nitrogen) so that the resolution can be increased without causing a decrease in depth of focus in the same manner as in the case of using a short-wavelength light source or a high NA lens. Since a resist pattern that exhibits a higher resolution and an excellent depth of focus can be inexpensively formed by liquid immersion lithography using a lens provided in an existing system, liquid immersion lithography has attracted attention.
However, it is considered that liquid immersion lithography can only be applied up to 45 nmhp. Therefore, technical development toward a 32 nmhp generation has been conducted. Moreover, a system (liquid immersion lithography system) used for liquid immersion lithography is very expensive, and may not be applied to a semiconductor production process.
A method that processes a given film formed on a first resist pattern to form a second resist pattern so that the film remains in the depression of the first resist pattern (Japanese Patent Application Publication (KOKAI) No. 2001-343757, for example), a resist pattern-forming method that forms a given film on a resist pattern formed by processing an upper-layer resist film formed on a lower-layer resist film (Japanese Patent Application Publication (KOKAI) No. 2002-110510, for example), a pattern-forming method that processes a processing target layer using a second patterning layer embedded to fill a first patterning layer formed by processing a resist layer formed on the processing target layer (Japanese Patent Application Publication (KOKAI) No. 2004-335873, for example), and the like have been disclosed as a method that enables finer patterning. However, a specific and practical method, material, etc. that improve such methods have not been proposed.